The present invention relates to fabrication methods of semiconductor memory devices; and, more particularly, to fabrication methods of ferroelectric memory devices, which can reduce the damage from plasma etching by using a pulsed-power technique.
By using ferroelectric material into capacitors in semiconductor memory devices, there have been proceeded the developments of the devices which can overcome the limitation of refresh present in the conventional DRAM (Dynamic Random Access Memory) devices and have large capacitance of memory. FeRAM (ferroelectric random access memory) devices as non-volatile memory devices can store information even at the condition of power off and also are equitable in operating speed to the conventional DRAM. So, they are promising as a future generation of storage devices.
Thin films of SrBi2Ta2O9 (hereinafter, referred as SBT) and Pb(Zr,Ti)O3 (hereinafter, referred as PZT) are mainly used as capacitance material in FeRAM devices. The ferroelectric materials have hundreds or thousands of dielectric constant at room temperature and two stable remanent polarization states. So, they are applied to the practices of nonvolatile memory devices with the states of thin films. The nonvolatile device with the ferroelectric thin film uses the principle that if an electric field is applied to the device to adjust the orientation of polarization and to input a signal, then the orientation of remanent polarization remained when the electric field is removed makes the digital signal 1 or 0 be stored in the device.
After completed with the formation of a capacitor comprising of a bottom electrode, a ferroelectric thin film and a top electrode, an oxide layer for interlayer insulating is formed over the entire structure and selectively dry-etched to form contact holes exposing the top electrode and the bottom electrode.
In the conventional fabrication method of FeRAM device, the dry etching is performed with plasma generated by RF (radio frequency) or micro power of hundreds kHz or several GHz. This method necessarily induces electrical or physical damage in the device.
In case of DRAM, the etching damage from plasma may be recovered in any later thermal process, so it does not result in problems. However, in case of FeRAM using ferroelectric material such as SBT, the ferroelectric characteristics may be easily deteriorated with the plasma. This deterioration results in decreasing the reading and writing performances of FeRAM and reducing the lifetime of the device. Thus, a separate thermal treatment for recovering the ferroelectric characteristics should be performed at about 700xc2x0 C. for about 30 minutes.
Accordingly, there are required process developments, which can reduce the damage of ferroelectric layer generated during dry etching with plasma for the oxide layer covered over the capacitor.
It is, therefore, an object of the present invention to provide a method for fabricating ferroelectric memory devices, which can prevent the deterioration of ferroelectric characteristics generated from conventional dry etching with continuous wave plasma for interlayer-insulating layer for forming capacitor contact.
In accordance with an embodiment of the present invention, there is provided a method for fabricating a ferroelectric memory device, which comprises the steps of forming an interlayer-insulating layer over the entire structure completed with the formation of a ferroelectric capacitor including a bottom electrode, a ferroelectric layer and a top electrode; and selectively etching the interlayer-insulating layer with pulsed-power plasma to form a contact hole exposing the top electrode of capacitor.
In accordance with another embodiment of the present invention, there is provided a method for fabricating a ferroelectric memory device, which comprises the steps of forming a first interlayer-insulating layer over the entire structure completed with the formation of transistor; forming a capacitor which includes a bottom electrode, a ferroelectric layer and a top electrode and in which the ferroelectric layer and the top electrode are superimposed on a part of the bottom electrode; forming a second interlayer-insulating layer over the ferroelectric capacitor; and selectively etching the second interlayer-insulating layer with pulsed-power plasma to form a contact hole exposing the top electrode of capacitor.
The present invention is characterized in that the interlayer-insulating layer covering the capacitor is etched with time modulated plasma, namely pulsed-power plasma. The pulsed-power plasma has lower electron temperature and ion energy within the plasma than the conventional continuous wave plasma. This is because high energetic electrons in the plasma are cooled during plasma off-period when the main power is adjusted with several decades microseconds.